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Date: Mon, 14 Feb 2011 14:38:50 -0800
From: Venkatesh Pallipadi <venki@...gle.com>
To: Suresh Siddha <suresh.b.siddha@...el.com>,
Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>,
Nick Piggin <npiggin@...il.com>,
Tim Chen <tim.c.chen@...el.com>, Alex Shi <alex.shi@...el.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Venkatesh Pallipadi <venki@...gle.com>
Subject: [PATCH] sched: Wholesale removal of sd_idle logic
sd_idle logic was introduced way back in 2005 (commit 5969fe06),
as an HT optimization.
As per the discussion in the thread here
lkml subject - sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1
https://patchwork.kernel.org/patch/532501/
the capacity based logic in the load balancer right now handles this
in a much cleaner way, handling more than 2 SMT siblings etc, and sd_idle
does not seem to bring any adiitional benefits. sd_idle logic also has
some bugs that has performance impact. Here is the patch that removes
the sd_idle logic altogether.
The initial patch here - https://patchwork.kernel.org/patch/532501/
applies cleanly over the below change and provides a micro-optimization
for a specific case, where an idle core can pull tasks instead of a
core with one thread being idle and other thread being busy.
It will be good to get some data on whether this micro-optimization
matters or not.
Also, there was a dependency of sched_mc_power_savings == 2, with sd_idle
logic. Copying Vaidy to know the impact of this change there.
Signed-off-by: Venkatesh Pallipadi <venki@...gle.com>
---
kernel/sched_fair.c | 53 ++++++++++----------------------------------------
1 files changed, 11 insertions(+), 42 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 0c26e2d..932dc13 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2610,7 +2610,6 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
* @this_cpu: Cpu for which load balance is currently performed.
* @idle: Idle status of this_cpu
* @load_idx: Load index of sched_domain of this_cpu for load calc.
- * @sd_idle: Idle status of the sched_domain containing group.
* @local_group: Does group contain this_cpu.
* @cpus: Set of cpus considered for load balancing.
* @balance: Should we balance.
@@ -2618,7 +2617,7 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
*/
static inline void update_sg_lb_stats(struct sched_domain *sd,
struct sched_group *group, int this_cpu,
- enum cpu_idle_type idle, int load_idx, int *sd_idle,
+ enum cpu_idle_type idle, int load_idx,
int local_group, const struct cpumask *cpus,
int *balance, struct sg_lb_stats *sgs)
{
@@ -2638,9 +2637,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
for_each_cpu_and(i, sched_group_cpus(group), cpus) {
struct rq *rq = cpu_rq(i);
- if (*sd_idle && rq->nr_running)
- *sd_idle = 0;
-
/* Bias balancing toward cpus of our domain */
if (local_group) {
if (idle_cpu(i) && !first_idle_cpu) {
@@ -2755,15 +2751,13 @@ static bool update_sd_pick_busiest(struct sched_domain *sd,
* @sd: sched_domain whose statistics are to be updated.
* @this_cpu: Cpu for which load balance is currently performed.
* @idle: Idle status of this_cpu
- * @sd_idle: Idle status of the sched_domain containing sg.
* @cpus: Set of cpus considered for load balancing.
* @balance: Should we balance.
* @sds: variable to hold the statistics for this sched_domain.
*/
static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
- enum cpu_idle_type idle, int *sd_idle,
- const struct cpumask *cpus, int *balance,
- struct sd_lb_stats *sds)
+ enum cpu_idle_type idle, const struct cpumask *cpus,
+ int *balance, struct sd_lb_stats *sds)
{
struct sched_domain *child = sd->child;
struct sched_group *sg = sd->groups;
@@ -2781,7 +2775,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
local_group = cpumask_test_cpu(this_cpu, sched_group_cpus(sg));
memset(&sgs, 0, sizeof(sgs));
- update_sg_lb_stats(sd, sg, this_cpu, idle, load_idx, sd_idle,
+ update_sg_lb_stats(sd, sg, this_cpu, idle, load_idx,
local_group, cpus, balance, &sgs);
if (local_group && !(*balance))
@@ -3033,7 +3027,6 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
* @imbalance: Variable which stores amount of weighted load which should
* be moved to restore balance/put a group to idle.
* @idle: The idle status of this_cpu.
- * @sd_idle: The idleness of sd
* @cpus: The set of CPUs under consideration for load-balancing.
* @balance: Pointer to a variable indicating if this_cpu
* is the appropriate cpu to perform load balancing at this_level.
@@ -3046,7 +3039,7 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
static struct sched_group *
find_busiest_group(struct sched_domain *sd, int this_cpu,
unsigned long *imbalance, enum cpu_idle_type idle,
- int *sd_idle, const struct cpumask *cpus, int *balance)
+ const struct cpumask *cpus, int *balance)
{
struct sd_lb_stats sds;
@@ -3056,8 +3049,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
* Compute the various statistics relavent for load balancing at
* this level.
*/
- update_sd_lb_stats(sd, this_cpu, idle, sd_idle, cpus,
- balance, &sds);
+ update_sd_lb_stats(sd, this_cpu, idle, cpus, balance, &sds);
/* Cases where imbalance does not exist from POV of this_cpu */
/* 1) this_cpu is not the appropriate cpu to perform load balancing
@@ -3193,7 +3185,7 @@ find_busiest_queue(struct sched_domain *sd, struct sched_group *group,
/* Working cpumask for load_balance and load_balance_newidle. */
static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);
-static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle,
+static int need_active_balance(struct sched_domain *sd, int idle,
int busiest_cpu, int this_cpu)
{
if (idle == CPU_NEWLY_IDLE) {
@@ -3225,10 +3217,6 @@ static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle,
* move_tasks() will succeed. ld_moved will be true and this
* active balance code will not be triggered.
*/
- if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
- !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
- return 0;
-
if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
return 0;
}
@@ -3246,7 +3234,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
struct sched_domain *sd, enum cpu_idle_type idle,
int *balance)
{
- int ld_moved, all_pinned = 0, active_balance = 0, sd_idle = 0;
+ int ld_moved, all_pinned = 0, active_balance = 0;
struct sched_group *group;
unsigned long imbalance;
struct rq *busiest;
@@ -3255,20 +3243,10 @@ static int load_balance(int this_cpu, struct rq *this_rq,
cpumask_copy(cpus, cpu_active_mask);
- /*
- * When power savings policy is enabled for the parent domain, idle
- * sibling can pick up load irrespective of busy siblings. In this case,
- * let the state of idle sibling percolate up as CPU_IDLE, instead of
- * portraying it as CPU_NOT_IDLE.
- */
- if (idle != CPU_NOT_IDLE && sd->flags & SD_SHARE_CPUPOWER &&
- !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
- sd_idle = 1;
-
schedstat_inc(sd, lb_count[idle]);
redo:
- group = find_busiest_group(sd, this_cpu, &imbalance, idle, &sd_idle,
+ group = find_busiest_group(sd, this_cpu, &imbalance, idle,
cpus, balance);
if (*balance == 0)
@@ -3330,8 +3308,7 @@ redo:
if (idle != CPU_NEWLY_IDLE)
sd->nr_balance_failed++;
- if (need_active_balance(sd, sd_idle, idle, cpu_of(busiest),
- this_cpu)) {
+ if (need_active_balance(sd, idle, cpu_of(busiest), this_cpu)) {
raw_spin_lock_irqsave(&busiest->lock, flags);
/* don't kick the active_load_balance_cpu_stop,
@@ -3386,10 +3363,6 @@ redo:
sd->balance_interval *= 2;
}
- if (!ld_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
- !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
- ld_moved = -1;
-
goto out;
out_balanced:
@@ -3403,11 +3376,7 @@ out_one_pinned:
(sd->balance_interval < sd->max_interval))
sd->balance_interval *= 2;
- if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
- !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
- ld_moved = -1;
- else
- ld_moved = 0;
+ ld_moved = 0;
out:
return ld_moved;
}
--
1.7.3.1
--
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